Embodiments of the present invention relate generally to the field of power supply control systems. Particular embodiments relate to the application of fuel cells for power generation. More particularly, embodiments of the present invention relate to the control of power supply to and from fuel cell systems used for primary or backup power supply.
Fuel cell systems can be employed as a reliable and efficient primary or backup power source for critical applications that normally use power drawn from the utility grid. A typical fuel cell system for electrical power includes a fuel cell stack which is the power generating component of the system, an inverter to convert the direct current produced by the fuel cell stack to an alternating current, a fuel source, for example in a solid oxide fuel cell system (SOFC) typically a hydrogen or hydrocarbon fuel, and a number of components, such as heat exchangers, valves, blowers, etc., designed to ensure the proper functioning of the power generation components, often referred to as the “balance of plant”. The balance of plant components can be powered by utility grid power rather than by the fuel cell stack.
A SOFC backup power system, for example, can be regeneratively coupled to the utility grid. This means that the fuel cell can provide power to the primary application if the grid goes offline or, when the grid is functioning normally, the fuel cell can reverse cycles and regenerate fuel for operating the system, or function as a current source for the grid.
In grid interconnected systems, it is important that a power source be applied to the balance of plant loads in a short period of time in the event of grid failure, otherwise there may be damage to the fuel cell stack. Unfortunately, it has been seen that mechanical contactors are often too slow to provide backup power to the balance of plant loads in the event of grid loss. In the past, this problem has been alleviated by means of an uninterruptible power supply (UPS), having batteries and other storage devices such as capacitors. Uninterruptible power supplies are, however, expensive and cumbersome to implement.